Definition: A type of conjoined twin united on any portion of the cranial vault or calvarium not involving the foramen magnum, skull base, face, or vertebrae. The juncture is rarely symmetric and may involve the entire head or only a portion and may include the meninges, venous sinuses, and the cerebral cortex. Infinite variations exist in both axial and rotational orientation. Type 1, twins are facing the same direction; type 2, twins are facing the opposite direction; type 3, twins are facing 90° from one another.
[cranio- + G. pagos, something fixed]
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